New Hot Tub some chemical Issues


I have a new Hot Tub made by Master spas Clarity Model 500 gallons. Really trying to follow Nitros Sticky for Chlorine in a hot tub but having 2 main issues.

1. I am having a really hard time keeping up with FC demand- Some days I add 6-8oz of Chlorine 10% . The next day 24 hr later FC = 0?
2. The second thing is relationship between PH and TA. When I get the TH around 80 ppm the PH goes above 7.8 and than I lower PH with Acid and TA also drops.
Do I just worry about PH first and than try to get my TA in line?
Any help would be appreciated.

FC = 0-1
CC= 0-1
PH = 7.8
TA goes between 70 - 80
CH = 250
CYA = 20
Borates = 50 Not tested just added based on Pool Calculator
Tub used almost every night 2 people for 45min to 1 hour.


Well-known member
Feb 17, 2017
Dahlonega, Georgia
If there is no one in the tub for 24 hours, 6 oz of 10% liquid chlorine would put you above 10 ppm and if you're back down to 0 in 24 hours, without anyone using the tub, that is way too much chlorine demand. On the other hand, if you soak 2 people for one hour at 102 deg F during that 24 hour period, then your chlorine demand would be about normal as bather waste will take up the majority of the chlorine. So what you describe doesn't tell us enough about the situation to know for sure. It would be a good thing to test chlorine demand over a 24 hour period without using the tub, so you'll know if you have a problem or not. For instance, if you start at 10 ppm and 24 hours later you are at 5 ppm, then your chlorine demand is 50% which is rather high. In a really clean tub, you might have chlorine demand as low as 10% to 20%, and 30% would be quite acceptable. If you have high chlorine demand, it means something is neutralizing the chlorine, and that would suggest biofilm in the plumbing. So it's pretty important to know.

The higher the TA, the more pH will rise. If you are having pH push up, you can lower total alkalinity to around 50 ppm and it might slow or stop the pH rise. The borates you have should help keep the pH stable too.

ant 83

Well-known member
Nov 3, 2015
appleton wisconsin
I suggest you confirm what pool math is telling you verses what is labeled on that bottle of chlorine.

test before and after you add chlorine. Check your work.

what it say on the bottle ain't the same as what does to your water.

Liquid chlorine loses strength.

The higher the temp, the faster.

The higher the strength of the chlorine, the faster.

There are other factors (sunlight,PH) but mostly, in my experience, it's weak, compared to what is says.


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Aug 10, 2012
FL panhandle
Lower your TA to 50 and then add 50 ppm of borates. Then when pH rises to 8.0 lower it to 7.6. As long as pH is below 8.0 it is fine.

Did you add 30 ppm of CYA?

Adding chlorine depends on how many person hours of soak time and how much stuff is on those persons like lotion, dirt, residual laundry products in swimsuits, etc. We don't use much lotion or any fabric softeners, etc if we wear a swimsuit. We add 2 oz of bleach (1/4 cup) per person hour in the tub which is 4.1 ppm in my tub. If we are in the tub for an hour or less I just always add 3 quarter cups (12.3 ppm). Which is shock level for a CYA of 30 ppm, [FC/CYA][/FC/CYA].

It is important to test FC before getting in the tub to make sure it isn't 0, when you get out of the tub to make sure you add enough bleach and then an hour or so later to see if you need to add more bleach, I like at least 3 or 4 ppm at this point. The test an hour later is the most important one because it tells you if you added enough bleach when you got out. If UFC is 0 then add at least 4 or 5 ppm and test again an hour later. And add more next ti e you get out of the tub. Once you learn the chlorine consumption in your tub for your situation it becomes pretty routine. The goal is to add enough bleach after you get out to have at least 2 or 3 ppm the next time you test or get in the tub. And, as with pools, it is safe to get in the tub with FC up to shock level for your CYA based on the [FC/CYA][/FC/CYA]. So, up to 12 ppm FC with CYA at 30 ppm.

One of the tricky things about a hot tub is if you get out of the tub after an hour and the FC is 0 then adding 4 or 6 ppm FC is likely not enough because there is enough bacteria and person waste in the water to use up that chlorine in an hour or less leaving no chlorine j the water and still leaving so e contaminants behind. You have to add enough chlorine to oxidize all the bathers waste and leave a few ppm chlorine behind. So, if we sit in the tub for 3 hours watching TV I'll add 6 quarter cups of bleach (24.6 ppm) and then check again in an hour.
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